Recently, pressure sensors are in wide use, varying from industrial plants to domestic electrical appliances. In particular, since a semiconductor pressure sensor utilizes both excellent mechanical characteristics of silicon and high productivity of semiconductor manufacturing techniques, it has become an indispensable component when used in combination with a microcomputer, for automatic control system which is moving towards intelligence and high efficiency. Generally, a semiconductor pressure sensor can be classified into a piezoresistance type and a capacitance type. The piezoresistance type pressure sensor uses a piezoresistance effect of silicon, and applies a method of detecting a diaphragm curve as a change of resistance amount in diffusion resistance. This sensor is produced in the usual semiconductor manufacturing process. On the other hand, the capacitance type pressure sensor applies a system of picking out a capacitance change between a fixed electrode and a diaphragm as an electric signal, and this type of sensor has high sensitivity and good temperature characteristics.
Also recently, along with the demand for improvements in controlling stability and safety in the field of automobiles, suspension brake systems and air bag systems have gradually come into wide use. Therefore, there is a great demand for an acceleration sensor, and the development of a semiconductor curved gage type acceleration sensor or a capacitance type acceleration sensor which is small, light, and highly reliable has been promoted. Furthermore, also in the fields of magnetic disks and light disks, there is a demand for a small, light, and highly reliable acceleration sensor for the purpose of controlling pick-up and access.
Generally, a capacitance type pressure sensor is superior to a piezoresistance type pressure sensor in resolution. Therefore, when the piezoresistance type pressure sensor is used to conduct a micropressure measurement with the same resolution as that of the capacitance type pressure sensor, a diaphragm must be formed even thinner than a conventional one. However, it is difficult to form a thin diaphragm by etching silicon chemically with semiconductor manufacturing techniques. Even if the thin diaphragm were formed, it must be handled with care and is easy to break. As a result, it was actually impossible to manufacture a piezoresistance type pressure sensor having the equivalent resolution as that of the capacitance type pressure sensor. Therefore, the capacitance type pressure sensor is considered to be suitable for measurement in a micropressure area of 100 gf/cm.sup.2 or less. However, also in this case, it was necessary to apply micromachining techniques to form the diaphragm. This was a problem, since these processing techniques were complicated and extremely costly. On the other hand, the capacitance type pressure sensor using a stainless diaphragm has been sold on the market, but this sensor has a defect of being easily affected by disturbance such as parasitic capacity. Thus, in order to achieve high accuracy, the problems existed that the sensor tends to become larger and more expensive.
In general, an acceleration sensor is known in the form of a semiconductor system of the piezoresistance type and capacitance type, and also in the form of a piezoelectric system using a piezoelectric substance. However, regardless of which system is used, a compact size and high sensitivity of the acceleration sensor can be attained only by the use of advanced mechanical characteristics of sensing parts, such as diaphragm, cantilever etc. In order to form the diaphragm and cantilever, highly fine processing techniques, for example micromachining techniques, are required. This was a problem, since these processing techniques lead to highly advanced or extremely costly techniques. As a matter of fact, the manufacturing cost does not pay at present, so that these techniques have not been put into practical use.